migrate iSCSI block volumes from democratic-csi to Proxmox CSI [ci skip]

Replace TrueNAS iSCSI (democratic-csi) with Proxmox CSI plugin for all
block storage PVCs. Eliminates double-CoW (ZFS + LVM-thin) and removes
the iSCSI network hop for database I/O.

New stack: stacks/proxmox-csi/ — deploys proxmox-csi-plugin Helm chart
with StorageClass "proxmox-lvm" using existing local-lvm thin pool.

Migrated PVCs (12 total):
- Phase 1 standalone: plotting-book, novelapp, vaultwarden, nextcloud, prometheus
- Phase 2 StatefulSets: CNPG PostgreSQL (2), MySQL InnoDB (3), Redis (2)

All services verified healthy post-migration.

stacks/redis/modules/redis/main.tf

@@ -59,7 +59,7 @@ resource "helm_release" "redis" {
     master = {
       persistence = {
         enabled      = true
-        storageClass = "iscsi-truenas"
+        storageClass = "proxmox-lvm"
         size         = "2Gi"
       }
 
@@ -79,7 +79,7 @@ resource "helm_release" "redis" {
 
       persistence = {
         enabled      = true
-        storageClass = "iscsi-truenas"
+        storageClass = "proxmox-lvm"
         size         = "2Gi"
       }